2.2.52 [HTML] Section 18.2.1, The SCRIPT element


The specification states:

 defer [CI] (case-insensitive)
 When set, this boolean attribute provides a hint to the user agent that the script 
 is not going to generate any document content (e.g., no "document.write" in 
 javascript) and thus, the user agent can continue parsing and rendering.

All Document Modes (All Versions)

If an author incorrectly adds document.write() within a deferred script tag, only the script-generated content will be displayed. Rendering of the remainder of the page will fail.